1. Field of the Invention
The present invention relates to a system and method for controlling a variable displacement engine during starting.
2. Background Art
Fuel economy for a multi-cylinder internal combustion engine can be improved by deactivating some of the engine cylinders under certain operating conditions. Reducing the number of operating cylinders reduces the effective displacement of the engine such that it is sometimes referred to as a variable displacement engine. Depending upon the particular configuration of the variable displacement engine, one or more cylinders may be selectively deactivated to improve fuel economy under light load conditions, for example. When one or more cylinders are deactivated, fuel and spark are not provided to those cylinders and the associated intake/exhaust valves are not operated and therefore remain closed. In some engine configurations, a group of cylinders, which may be an entire bank of cylinders, is selectively deactivated under appropriate operating conditions.
Fuel economy and emission benefits may be associated with starting and operating a variable displacement engine with one or more cylinders deactivated. However, cranking and starting the engine with at least some of the cylinders deactivated using conventional control strategies may result in slower crank speeds and associated harshness that is undesirable for many drivers. The inventors herein have recognized that crank/startup harshness may be due to the xe2x80x9cair springxe2x80x9d effect of the deactivated cylinders and the stopping position of the crankshaft.
The present invention provides a system and method for controlling a variable displacement engine during cranking and starting. In carrying out various objects, advantages and features of the invention, a system and method for controlling a variable displacement internal combustion engine during cranking and starting include a hybrid operating mode to allow intake/exhaust valve operation while preventing fuel delivery or spark, or both, for at least one of the subsequently deactivated cylinders or bank of cylinders during cranking and starting.
The present invention has a number of advantages relative to conventional starting control of variable displacement engines in either the partial or full activation modes. For example, the present invention provides less compression for the starter motor to overcome during cranking resulting in faster crank speeds and shorter start times. In addition, for some applications, not energizing the variable displacement mode solenoids to deactivate the intake/exhaust valves lessens the electrical load on the battery during cranking. The present invention reduces or eliminates crank stalls and generally results in less crank/startup harshness.
The above advantage and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.